Continuous plastic webs are manufactured for many purposes, e.g., flat sheets of discrete bottle labels, wherein each label is ultimately applied around a blow-molded plastic, or similar bottle. In the manufacture of webs of labels, it is important that manufacturing operations be accurately located along the web. Accordingly, it is important to accurately register the web with work stations on the machine performing operations on the web.
While there is reasonable latitude or tolerance in the location of any given operation on a web, there is a cumulative error problem which must be considered. When transferring printed indicia onto a web of labels, cumulative error cannot be tolerated in that over the passage of hundreds to thousands of feet of printed labels, if registration is not corrected, the printed indica will not be centered on the product onto which it is affixed. The cumulative error problem is exacerbated when the web is plastic in that plastics tend to stretch. Since it is virtually impossible to maintain constant web tension during printing and other manufacturing operations, stretching not only occurs, but it occurs unevenly.
Because of the cumulative error problem, it is customary to repeatedly register the web with stations where manufacturing operations are to be performed. One known technique is to provide clear spaces in a web between the repetitive printed indicia. These spaces function as windows into which a registration mark is imprinted. An optical detector is positioned to cyclically view the web. If the equipment is adjusted and functioning properly, each viewing of a cycle is concurrent with the passage of one of the windows past the detector. The detector senses the registration mark and causes the manufacturing operation to occur at a time coordinated with this sensing.
When printed decorative and informative indicia on the web are passing the detector, the detector is often "blinded" so that it will not see and be confused by the imprinted indicia. One solution to this problem is to cycle the detector in synchronism with the passage of decorative and informative indicia pass. A major problem with cyclical detection however is that if the web is out of registration when the detector is operative, the window of informative indicia may not be seen, and erroneous signals will be emitted by the detector, resulting in scrap. Thus, machine setup, and the restoration of appropriate registration of the machine which gets out of synchronism, is time-consuming and difficult.
The effectiveness of traditional registration marks for controlling operations even on essentially a clear web, a web which is not printed except for the visible "eye" marks, is also limited with respect to accuracy of detection. The accurate detection of such registration marks is dependent on either, the largeness of the mark or, in the case of a small mark, the accuracy with which the detector is registered upon the fluctuating paths in which the marks travel. The accurate detection of traditional eye marks affixed to a plastic or other flexible, stretchable, elastic web requires either: a large eyemark to insure that passage of at least some portion of each mark underneath a stationary detector; or in the case of small eye marks, a sophisticated detector tracking apparatus to insure the consistent registration of the detector upon the fluctuating paths of the moving marks.
One effort to improve over the use of "visible eyemarks" is described in U.S. Pat. No. 4,467,207 to Lerner et al., which teaches the use of organic polar or ionic material that emits wavelength-shifted radiation under incident electromagnetic radiation. The choice of a "polar" dye was indicated to be critical to the operation of the Lerner et al., invention in that migration of "non-polar" dyes was an issue, but not of "polar" dyes.
Specifically, various "polar" or "ionic" dyes show below were taught to be effective in the application. ##STR1##
As taught by Lerner et al., the migration of a dye is controlled by its solubility. Lerner determined that by using a polar or ionic dye, there would be no migration through the non-polar polymer films, thereby capitalizing on a system of "like/unlike", i.e., "polar or ionic dye/non-polar polymer film."
Another approach to maintaining appropriate registration between a web and various work stations is to provide a marginal registration strip with printed or other registration markings. While such an approach can simplify machine set up and registration, as compared with the cyclically blinded detector approach, the strip is trimmed off and becomes scrap so this process is wasteful.
A variation in the technique for controlling the web movement with a removable strip employs gaps or holes positioned along the strip as position indicators for the web. The presence of the gap is detected by a spark-gap detector which completes a circuit by causing a spark to traverse the gap. In this way, the presence of absence of gaps or holes along the web is indicated to control circuitry which in turn is used for maneuvering the web.
The spark-gap system for web control also has deficiencies. In order to complete a circuit with the use of a spark, it is necessary that a relatively high voltage be maintained between two portions of the spark-gap detector. In some environments, this can be very undesirable. For example, moisture can either cause a malfunction of the spark-gap detector or provide a path of low electrical resistance which results in a false signal. A second problem encountered is that the detector cannot tell the difference between intentionally and unintentionally formed gaps or holes. If the control circuitry is activated by the presence of a rip in the registration strip of the web, control functions will be unsynchronized and web material will be wasted.
It has been suggested, that magnetization of an area directly on the web with a decorative coating printed over the magnetized area can be used to provide a non-visible control function to the moving web. Magnetized areas are susceptible to detection by various known techniques and have been proposed for providing control coordination. A magnetized area, however, can be affected by its environment in an adverse manner. Electric and magnetic fields in the area of the moving web could create a condition where the detector would not detect the magnetized area and control coordination would be lost. Further, if the magnetized area is placed directly on the web, it is virtually impossible to hide the magnetized area with a printing overlay and with clear webs, the area will be visible from the other side of the web. Thus, a magnetized area detracts from an intended and desired attractive appearance.
However, what is needed in the industry, is both a visible and ultraviolet registration technology for use in flat sheet label applications using existing equipment, optionally using one of the printing decks for ultraviolet ink application, or when this is not possible due to existing printing requirements on the label and the limitations of the physical number of printing decks on the machine, using a naturally ultraviolet fluorescing pigment in one of the printing decks, thereby serving to utilize one deck for both ultraviolet and visible marking. Alternately, an ultraviolet fluorescing system which did not migrate, yet which was a "like/like" combination, i.e., "non-polar or non-ionic pigment/non-polar polymer film" would be unexpected and opposed to the teachings of the Prior Art.